There is a nationwide recognition of the public health challenges arising from the incidence and prevalence of chronic pain. In 2017, the National Academies of Sciences published a landmark review of the literature and found conclusive evidence that cannabis can be an effective treatment for chronic pain. To date, 31 states and the District of Columbia have adopted medical cannabis laws (MCLs) legalizing either home cultivation or dispensary-based sales of cannabis for qualifying medical conditions. However, little is known about substitution away from medical treatment of pain when MCLs go into effect, or the impact such substitution has on other health care utilization. The goal of the current study is to examine the association between MCLs and health care utilization for patients with chronic non-cancer pain enrolled in public and private insurance plans. Using the National Institutes of Health 2015 National Pain Strategy as an organizational framework, we will conduct a retrospective, longitudinal, analysis of the difference in prescription medication and pain-related health service utilization in a cohort of patients with chronic pain in states with and without MCLs. In addition, we will conduct sub-analyses for patients living in rural compared to urban areas, and will examine the relationship between MCLs and health care utilization for patients with neuropathic versus nociceptive chronic pain. We will analyze patient-level panel data measured quarterly. Data for this study will come from a sample of privately insured individuals from the Health Care Cost Institute comprehensive claims databases (N ? 40 million covered lives; 2015-2019) and two separate samples of publically insured individuals from Medicare (N ? 5 million enrollees; 2011-2018) and Medicaid (N ? 5 million enrollees; 2011-2017) claims databases. We will employ a series of difference-in- differences regressions estimated separately for each of the insured groups. Our key policy variables will be a measure of any implemented MCL, measures of implemented MCLs by type (dispensary, home-cultivation-only, or THC oils). Individual patient characteristics, county and state demographics, and a series of fixed effects at the state and quarter level will be used as controls in all models. We will also control for policy endogeneity where necessary. Chronic pain and the opioid epidemic are clear public health crises. Preliminary evidence suggests that access to medical cannabis can alter prescription pain medication use. It is thus essential to understand the relationship between MCLs and health care utilization for chronic pain patients in order to optimize public policies and to provide guidance to clinical practitioners on likely patient responses to MCL implementation.